1. Field of the Invention
The subject invention relates to master cylinders for automotive brake assemblies and more specifically to an improved master cylinder having a compact profile.
2. Description of the Prior Art
Master cylinders for automotive brake assemblies are well known in the art. The master cylinders typically have a hollow body defining an inner bore which receives primary and secondary pistons. Brake fluid is passed into and out of the bore by actuation of the pistons to facilitate a hydraulic braking system. In particular, selective movement of a brake pedal moves the primary and secondary pistons within the bore and develops elevated hydraulic pressure which is transmitted to vehicle wheel cylinders or calipers causing the brakes to be applied. The master cylinder therefore provides the function of responding to an application of force through the brake pedal to build pressure in the hydraulic braking system. Additionally, the master cylinder controls the flow of fluid between the brake hydraulic system and a reservoir.
A typical master cylinder is generally combined with a hydraulic or vacuum operating power booster. The power booster assists in increasing the amount of force applied to the master cylinder""s pistons through a push-rod upon actuation of the brake pedal. Therefore, the master cylinder is generally constructed of a rigid structural material sufficient to carry the load imposed thereon by the push-rod. In particular, master cylinders have generally been formed of a cast iron or cast aluminum. Examples of cast iron or cast aluminum master cylinders are shown in U.S. Pat. Nos. 3,937,020 and 5,604,969. The cast iron or cast aluminum master cylinders are then machined to meet design requirements. The finish machining is a time consuming and expensive process that often unveils porosity, which interrupts surface smoothness and can create leaks in the braking system.
One improvement to the cast iron or cast aluminum master cylinders is set forth in U.S. Pat. No. 5,590,527, wherein the body of the master cylinder is linear extruded. The linear extruded master cylinder has certain manufacturing and assembly advantages. However, due to the limitations associated with linear extrusions, the end wall and flange must be separately mounted to the extruded body. This adds to the overall cost of assembling the master cylinder. In addition, the profile of the master cylinder, as viewed in cross-section, is substantially asymmetrical which prevents the master cylinder from be manufactured by other more efficient techniques such as impact extrusion.
Impact extrusion typically places a lubricated slug of material into a die and then the slug is struck with a punch. The material is forced into conforming with the die and the punch which produces the desired configuration. Impact extrusion, however, requires that the final product have a compact profile. Products with substantial asymmetric profiles cannot the formed by this process. Hence, the prior art master cylinders have not been able to be formed by this process.
Accordingly, it would be desirable to provide a master cylinder that does not suffer from the deficiencies associated with cast iron, cast aluminum, or linear extruded master cylinders yet maintains the necessary structural integrity to withstand the loads imposed thereon. Even more preferably, it would be desirable to develop a master cylinder which has a compact profile that can be formed by an impact extrusion process.
The subject invention provides a master cylinder having a compact profile. In particular, the master cylinder comprises a hollow body having a continuous outer wall extending between first and second ends to define a longitudinal bore formed between the ends. The outer wall has a continuous thickness between the ends when viewed in cross-section and further defines at least one mounting surface on an exterior thereof. The longitudinal bore has an inner diameter defining an inner surface. An end wall is integrally formed with the outer wall at the first end to close an end of the bore. At least one aperture is formed within the outer wall at the mounting surface to provide fluid communication between the outer wall and the bore. A flange is integrally formed with the outer wall at the second end to define a fully integrated master cylinder. The outer wall further defines at least one thickened section extending between the inner surface of the bore and the mounting surface with the thickened section being at least 30 percent smaller than the inner diameter of the bore for providing the compact profile of the integrated master cylinder.
The subject invention also provides for a method of manufacturing a master cylinder having the hollow body with the end wall and the flange. The method comprises the steps of: extruding the hollow body to define a continuous outer wall extending between first and second ends having a longitudinal bore formed between the ends; forming the end wall on the first end of the outer wall simultaneously with the extrusion of the hollow body to close an end of the bore; positioning the flange over at least a portion of the second end of the outer wall; deforming a distal portion of the second end of the outer wall; and interlocking the second end of the outer wall with the flange during the deforming of the distal portion to integrally mount the flange to the hollow body.
Accordingly, the subject invention provides for a master cylinder having a compact profile such that the master cylinder, having the end wall and flange, may be completely formed from an efficient impact extrusion process. In addition, the subject invention provides for a unique method of attaching a flange to the body of the master cylinder. The master cylinder of the subject invention can therefore be efficiently manufactured, with less material, cost, and weight, easily assembled, and has sufficient structural integrity to withstand the loads imposed thereon.